Harden implicit scope computation against CyclicReference errors.

Author: odersky

src/dotty/tools/dotc/core/Contexts.scala

@@ -170,7 +170,11 @@ object Contexts {
       if (implicitsCache == null )
         implicitsCache = {
           val implicitRefs: List[TermRef] =
-            if (isClassDefContext) owner.thisType.implicitMembers
+            if (isClassDefContext) 
+              try owner.thisType.implicitMembers
+              catch {
+                case ex: CyclicReference => Nil
+              }
             else if (isImportContext) importInfo.importedImplicits
             else if (isNonEmptyScopeContext) scope.implicitDecls
             else Nil

src/dotty/tools/dotc/core/Types.scala

@@ -2976,7 +2976,7 @@ object Types {
       val ex = new CyclicReference(denot)
       if (!(ctx.mode is typer.Mode.CheckCyclic)) {
         cyclicErrors.println(ex.getMessage)
-        for (elem <- ex.getStackTrace take 40)
+        for (elem <- ex.getStackTrace take 50)
           cyclicErrors.println(elem.toString)
       }
       ex